1. Field of the Invention
The present invention relates to the field of specimen analysis, and methods and apparatus therefor. More particularly, the invention relates to the field of specimen analysis for monitoring and controlling industrial, agricultural, mineral exploration and similar processes and operations.
2. Description of the Related Art
The need to monitor or control an operation or process arises in many industrial operations. Such industrial operations include the manufacture of goods, and the exploration for and production of minerals. Frequently, the data required to monitor or control an operation or process is generated by a chemical analysis that determines the presence or quantity of certain materials. These materials may be used in the process, or they may be undesirable contaminants. For example, some fluids used in manufacturing environments are cycled through an entire factory and used in multiple locations therein. The effectiveness of the fluids may rely on the presence of multiple additives therein, which are exhausted over the course of use, and must be replenished. The determination of when to replenish the additives, and in what amount, is often left up to a technician who takes a sample of the fluid and analyzes it using manual, visual titration techniques to determine the quantity of different additive materials present. Each sample is analyzed for the presence or absence of one or more specific materials desired to be present in the fluid, and the quantities thereof in the sample dictate whether to add additives to the fluid, and if so, the amounts of additives to add to the fluid to restore it to its intended composition. Errors inherent in this analysis, which relies upon the judgment of the technician to determine the quantities of additives in the samples, can result in inadequate or improper addition of the additives, resulting in decreased performance of the fluid for its intended purpose. Likewise, some fluids used in manufacturing processes may become contaminated with undesirable materials. For example, it may be illegal to discharge fluids from industrial, chemical, mineral exploration and other sites when those fluids contain certain levels of hazardous materials. Therefore, the discharged fluid must be analyzed for the presence and quantity of those hazardous materials. In many industrial settings, this analysis is again made manually, typically through visual titration techniques, and errors in the analysis can result in the unwanted discharge of hazardous materials, or the perceived inability to discharge fluid streams that are properly dischargeable.
Microfluidic devices, which are widely used in the analysis of biological materials, have not been widely used to analyze samples from industrial processes. Microfluidic devices are devices comprising fluidic elements that have at least one fabricated dimension in the range of from about 0.1 μm to about 500 μm. Fluidic elements are structures through which fluid can flow, such as passages, channels, chambers or conduits. So the fluidic elements in microfluidic devices typically have at least one internal cross-sectional dimension (e.g., depth, width, length, diameter, etc.) between about 0.1 μm and about 500 μm. Microfluidic devices have found a wide range of applications in the analysis of biological materials. For example, microfluidic devices have been employed to perform various analyses on nucleic acids such as RNA and DNA, to screen biological samples for therapeutic properties, and to determine the concentration of certain ions within a cell. The use of microfluidic devices has been almost exclusively limited to the analysis of biological materials largely because the concentration of the components of interest in biological samples, and the pH of those samples, are within relatively narrow and predictable ranges. Having the concentration of components of interest within a narrow and predictable range allows the concentration of reagents used in an analysis to be predetermined before the analysis is performed. For example, many fluorescent dyes used to label components of interest in an analysis are only effective over a certain concentration range of the material the dyes detect. In general, the dyes are only effective with trace concentrations of the materials of interest. More specifically, a fluorescent dye can be used to quantify the concentration of the material detected by the dye when the intensity of fluorescence of the dye predictably varies with the concentration of the labeled material. However, fluorescent dyes only have a limited dynamic range, meaning that the level of fluorescence is indicative of the concentration of the material over a narrow range of concentration. Similarly, many of those fluorescent dyes are only effective within a certain range of pH. Thus it would be very difficult to employ a fluorescent dye to analyze a sample in which the pH and the concentration of the material of interest is completely unknown, as is typically the case for samples of fluids from industrial operations. Nevertheless, it would be desirable to employ microfluidic devices to analyze those fluids because analyses carried out in microfluidic devices are rapid, precise, and easily automated. Another factor limiting the application of microfluidic devices to the analysis of industrial fluids is that the level of fluorescence generated by a sample may vary between individual microfluidic devices. Thus an individual device would have to be calibrated before the device could produce accurate data.
Thus, there is a need in the art for methods and apparatuses for analyzing fluids used in industrial processes that are not reliant on human judgment and skill for the analytical result, and that have greater reproducibility. This need could be satisfied through the application of microfluidic devices.